Internal combustion burner, particularly for drawing mineral fibers

ABSTRACT

An internal combustion burner, especially for attenuation of mineral fibers, and including a combustion chamber, into which at least one duct for feeding fuel and oxidizer opens, and provided with an expansion orifice. The combustion chamber is provided with at least one flame stabilizing element, the geometry of the walls of which is chosen to create a confinement zone in which at least part of the combustion between oxidizer and fuel takes place.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an internal combustion burner capable ofproducing high-velocity gas streams at high temperature. Moreparticularly, the invention relates to burners that are used inprocesses for forming mineral fibers, in which the attenuation of thefibers results from the gas streams emitted by said burners alone or incombination with other means such as centrifuging means orspinneret-type attenuation means. For further details about fiberizingprocesses using a spinner (internal centrifuging), reference may be madeto patents WO 99/65835, WO 97/15532, FR-2 677 973, FR-2 576 671, FR-2524 610, FR-2 801 301, FR-2 576 671, EP-189 354 and EP-519 797. Forfiberizing by what is called external centrifuging or fiberizing with arotor, reference may be made to the following patents: EP 991 601, WO97/0396, WO 97/0395 and EP 465 310.

2. Discussion of the Background

Ideally, this type of burner must meet a large number of requirements asclosely as possible: It must be safe and reliable. It must also have themost stable operating conditions possible, especially having a flamethat does not risk being blown out, a flame that is well contained and“attached” in the combustion chamber. It is also desirable for theburner to have the least possible inertia, i.e. for it to have operatingconditions that are easy to modify. The aim is also for it to be ofmaximum durability, to be not too complicated to manufacture, and to becompact. Moreover, it must be able to be easily fitted to the fiberizingdevices with which it is combined and easily tailored to thecompositions of the materials to be fiberized (which compositionsdetermine their hot behavior, most particularly their viscosity) and tothe type of mineral fibers that it is desired to obtain (especiallytheir dimensional characteristics).

SUMMARY OF THE INVENTION

All these sometimes conflicting requirements have resulted in theconstruction of various types of internal combustion burner.

One useful burner is described in detail in patent EP-0 091 380 B1: Thecombustion chamber is fed with an oxidizer/fuel mixture and its walls,which are made of refractory cement having small asperities, are usedfor “attaching” the flame in order to stabilize it. The combustionchamber is also profiled so that the burnt gases follow a relativelylong path along the curved walls of the combustion chamber so as toreduce the “inert” zones of the combustion chamber, that is to say zonesin which a certain amount of gas could be more or less immobilized.

This burner operates satisfactorily. However, it has certain limitationsintrinsic to its design. Thus, it operates well when relativelystandard, that is to say quite high, burner outlet gas temperatures areintended, for example 1500 or 1600° C. However, it is more difficult toobtain perfectly stable operating conditions when lower burner outletgas temperatures are intended, for example around 1400° C. To lower thetemperature, it is possible to add oxidizer (air) to the air/gas mixturefeeding the combustion chamber, but this “dilution” has limits beyondwhich there is a risk of the flame being extinguished. This burneroperates within operating conditions constrained by both temperature andpressure parameters at the burner outlet. The operating pressure rangeis “narrow” and such a configuration does not allow this working rangeto be broadened since, at low pressure, fluctuation phenomena induced byinstability of the combustion conditions in the burner occur. At highpressure, there would be a risk of the flame “detaching” from the burnerand being “blown out”.

It is therefore an object of the invention to improve internalcombustion burners, especially so as to overcome the abovementioneddrawbacks. Its aim in particular is to obtain burners that are moreflexible in operation and more adaptable in terms of gas temperature,velocity and flow rate ranges at the burner outlet. A secondary aim isto preferably obtain burners that are of low inertia, have stableoperating conditions and are reliable.

A subject of the invention is firstly an internal combustion burner,especially for the attenuation of mineral fibers, comprising acombustion chamber, into which at least one duct for feeding fuel(s) andoxidizer(s) opens, and provided with an expansion orifice. Thecombustion chamber in question is also provided with at least one flamestabilizing element, the geometry of the walls of which is chosen so asto create a confinement zone in which at least part of the combustionbetween oxidizer(s) and fuel(s) takes place.

To effect combustion, the inventors have in fact adapted, and put intoconcrete form, the combustion principle of an afterburner chamber of anaircraft engine. In that technology, there are several flames that areheld “attached” in the hot part of the afterburner chamber, with a kindof channel called a “flameholder”. Even though the technical field ofthe invention is unrelated, the inventors have succeeded in transposingsuch flame attachment elements to a burner for attenuating mineralfibers. It has been found that the presence of such a flame stabilizingelement is extremely effective and therefore allows the operation of theburner to be stabilized, even under operating conditions that aresomewhat extreme, for example when the aim is to obtain burner outletgases that are particularly hot or, conversely, somewhat “cold” (theterms “hot” and “cold” being, of course, relative and to be consideredwithin the context of the technical field of the present invention, inwhich the temperatures are in any case at least 500 or 1000° C.).

Advantageously, it is within these confinement zones that most,preferably nearly all, or indeed all, of the combustion takes place.Thus, instead of the flame being attached to the walls of the combustionchamber, as in the case of the burner described in the aforementionedpatent, the flame is attached to an additional element, which makes itpossible to control, concentrate and localize the flame at the desiredpoint in the combustion chamber. In fact, the flame stabilizer isadvantageously designed as regards its geometrical shape so as to keepthe zone referred to as the confinement zone in its “slipstream”, thiszone being a gas recirculation zone that will be explained in detailbelow, the residence time of these gases in this zone being long enoughfor the combustion to be maintained therein. The confinement zone mayalso be defined as a zone in which the gas velocity is lower than in therest of the combustion chamber. Fluid stagnation is created in thisconfinement zone, in which the combustion may be maintained.

This confinement/recirculation zone then constitutes a stable hot-gaszone that can continuously “release” a certain flow of burnt gases.

According to the invention, the internal combustion burner, especiallyfor the attenuation of mineral fibers, comprising a combustion chamber,into which at least one duct for feeding fuel(s) and oxidizer(s) opens,and provided with an expansion orifice, is characterized in that thecombustion chamber is provided with at least one flame stabilizingelement that has two solid walls substantially facing each other andjoined together at one of their ends by a solid end wall so as toconstitute a semi-open opening zone opposite the end wall, a confinementzone being created between the walls and near the opening, in whichconfinement zone at least part of the combustion between oxidizer(s) andfuel(s) takes place.

The location and the configuration of the flame stabilizer according tothe invention will be able incidentally to influence the way in whichthe burnt gases then circulate in the combustion chamber before they areexpelled via the expansion orifice. As mentioned above, the objective isgenerally for these burnt gases to occupy the maximum volume of thecombustion chamber.

Thus, it is advantageous for the flame stabilizer(s) to be placed nearthe internal wall of the combustion chamber. This is, in fact, afavorable configuration, enabling the burnt gases leaving theconfinement zone to be made to run along the wall of the combustionchamber and to “fill” it as much as possible during their travel insidethe combustion chamber.

The combustion chamber preferably comprises a plurality of stabilizers.Let us take the convention, for greater clarity, that the burneraccording to the invention is in a suitable position in combination withone or more fiberizing means of the spinneret or spinner dish. In thecase of a spinneret, which is presumed to be linear and placed in ahorizontal plane, the burner of the invention is placed near thespinneret, which is also in a linear configuration in an approximatelyhorizontal plane. In this case, the combustion chamber advantageouslyhas, in this horizontal plane, a parallelogram-type cross section, forexample a rectangular cross section. Furthermore, in this horizontalplane, the chamber preferably has at least two stabilizers side by side,and preferably at least (shape, size) five or ten, preferably uniformlyspaced apart. The horizontal cross section of the combustion chamber andthe number of stabilizers are to be selected so that it is possible togenerate sufficient hot gas at the spinneret outlet, over the entirelength of the latter.

In the case of a spinner “dish” (that is to say a spinner capable ofrotating about a generally vertical axis, fed with molten glass, and theperipheral loop of which is pierced by a plurality of orifices), theburner according to the invention preferably has a shape that isschematically annular, since it will, as it were, surround the spinnerdish. In the spinning position, and therefore in an approximatelyhorizontal plane, the cross section of the combustion chamber will begenerally annular and provided with stabilizers placed concentrically inthe chamber. Here, again, it is advantageous for these stabilizers to beuniformly spaced apart.

Whether the burner is a linear burner for a spinneret or an annular-typeburner for a spinner dish, the distance between two adjacent stabilizersis preferably chosen such that the streams of burnt gases emanatingtherefrom join up at a given distance from the stabilizers, to form aunified hot stream that is as homogeneous as possible.

Whether the burner is for a spinneret or for a spinner dish, thecombustion chamber in vertical cross section (again considering theburner in combination with the fiberizing members in the fiberizingposition) may have only a single stabilizer. According to anotherembodiment, it may have more than one of these in vertical crosssection, for example two, one “on top of” the other. Here, again, thedistance separating them is to be adjusted, especially so that the“sheets” of gases generated by each series of stabilizers (one seriesper horizontal plane) can advantageously interpenetrate. Preferably, thestabilizers of the various rows are arranged in a staggeredconfiguration, especially so as to facilitate the circulation of air(the oxidizer) from one row to another in order, if necessary, toprovide, among other functions, satisfactory cooling of all thestabilizers.

Advantageously, the flame stabilizer or stabilizers according to theinvention are mostly, especially essentially all, made of metal. Also,advantageously, the stabilizers are mounted in the combustion chambersuch that it is possible to adjust their positions, especially such thatit is possible to make them pivot about an axis, for example the axis ofthe inflow of fuel.

The geometrical shape of the stabilizers may vary a great deal, providedthat it makes it possible to define a confinement zone from which theburnt gases can escape. A geometrical shape having symmetry in a planeand/or along an axis may be chosen. The shape in question may especiallyhave two symmetries in two planes perpendicular to each other.

According to a preferred embodiment, the projection of its geometricalshape perpendicular to its plane of symmetry (or to one of its planes ofsymmetry if there are more than one of them) has the approximate shapeof a V or a U. According to another preferred embodiment, as analternative to or in combination with the previous one, its projectionperpendicular to its plane of symmetry (or to the other of its planes ofsymmetry if it has two of them) has the approximate shape of a trianglewith rounded corners, especially an approximately isosceles triangle.

We now come to the way in which the burner is fed with oxidizer and withfuel. Advantageously, at least one feed duct, fed with fuel(s) (of thenatural gas type) opens into the confinement zone of the flamestabilizer (or into at least one of them, if there are more than onestabilizer). The relative position of the outlet orifice of the duct andof the stabilizer is preferably chosen such that the gas (gases) is(are) sprayed against the walls of the stabilizer defining theconfinement zone. The combustible gas is thus forced to be optimallydistributed within the confinement zone. For example, the outlet orificeis placed between the walls and near the bottom of the stabilizer.Alternatively, the outlet orifice may be located at the front of thestabilizer, and so as to be offset with respect to its axis of symmetry,the stream of gas being directed toward the inside of the stabilizer.Both these configurations may be envisioned in the same burner, so it ispossible to choose one or other of the outlet orifices depending on thetemperature range at which the fiberizing is carried out. The terms“front” and “rear” referring to the stabilizer are defined below in thedescription as being close to the opening of the stabilizer and on theopposite side from the bottom of the stabilizer, and being on theopposite side from the opening and on the outside of the stabilizer soas to be opposite the bottom of the stabilizer, respectively. The feedduct may be supplied completely or almost entirely with fuel. It mayalso be supplied only predominantly or even only partially with fuel,the remainder consisting, for example, of oxidizer of the air type orother gases possibly participating in the combustion.

At the same time, it is advantageous to place the oxidizer (for exampleair, oxygen, oxygen-enriched air) feed duct(s) so that it (they) opens(open) into the combustion chamber in order to spray the oxidizer onthat side of the walls of the stabilizer that is opposite the side indirect contact with the confinement zone. Schematically, a preferredembodiment therefore consists in injecting the combustible gas into theconfinement zone, actually into the stabilizer or in front of thestabilizer, and in injecting the oxidizer (air) “behind” the flamestabilizer, in order to create a flow of oxidizer (air) that envelopsthe stabilizer, a variable portion of this air then being trapped in theconfinement zone. In this situation, in which the oxidizer and fuelfeeds are separate, the confinement zone will then have two purposes:The first is to provide oxidizer/fuel mixing, and the second to provideand maintain their combustion.

Here, again, the oxidizer feed duct may be fed 100% with oxidizer.However, it may also be fed alomost entirely, predominantly or partlyonly with oxidizer, the remainder consisting, for example, of fuel orany other gas possibly participating in the combustion.

It is thus possible to choose a gas feed duct that runs into thecombustion zone and is fed with an oxidizer/fuel gas mixture in variableproportions, and a feed duct opening out “behind” the stabilizer, asexplained above, which is itself fed predominantly with oxidizer of theair type: This inflow of oxidizer makes it possible, on the one hand, tomodify the oxidizer/fuel ratio in the confinement zone and, on the otherhand, if necessary, to “cool” the walls of the stabilizer.

As mentioned above, it is preferable for each stabilizer, when there aremore than one of them, to be associated with a feed duct containing fueland opening into its confinement zone. For example, a single feed ductcontaining oxidizer (typically, for example, 100% air, to take thesimplest operation) may “feed” several adjacent stabilizers by suitablepositioning and a suitable configuration (if it opens out “between” twoadjacent stabilizers for example, and/or if it has the form of aperforated rail or a lip).

It is also envisioned within the context of the invention to choose feedducts that convey an oxidizer/fuel mixture, the mixture having beenproduced before injection into the combustion chamber (anotherembodiment is that of one type of duct conveying 100% oxidizer or 100%fuel and the other an oxidizer/fuel mixture).

However, choosing oxidizer and fuel feed ducts that are separate ishighly beneficial from the industrial standpoint, for more than onereason: It avoids a prior mixing step, mixing taking place in situ inthe combustion chamber. Such eliminates any risk of the mixtureexploding in the burner feed ducts. Within the context, more specific tothe invention, of the use of the flame stabilizer, the characteristicsof the oxidizer and of the fuel may be varied separately: The air flowrate and the gas flow rate, and their relative velocities, may beadjusted independently of each other. In point of fact, in theembodiment described above, these are parameters that will optimize themixing of the two gases in the confinement zone. Thus, it will bepossible to have combustible gas injected at high velocity into theconfinement zone, which gas will be enveloped by a stream of oxidizer ofthe air type having, for example, a lower velocity. This creates acontrollable gas exchange, and therefore a mixture that can becontrolled and combustion between the two types of gases in this zonethat can be optimized.

As mentioned above, it is preferred to position the flame stabilizer(s)relative to the internal wall of the combustion chamber such that theburnt gases are forced to run along at least part of this wall,especially along a path approximately in the form of a loop. It istherefore beneficial to profile the internal wall in order to maximizethe path of the stream of burnt gases emanating from the confinementzone(s).

In the case of a burner suitable for a spinneret-type attenuating means,with the abovementioned conventions the geometry of the cavity definedby the walls of the combustion chamber may be the following:

-   -   in horizontal section, its cross section may be approximately of        rectangular shape;    -   in vertical section, its cross section may advantageously be at        least partially curved.

This may involve, for example, the juxtaposition of two portions ofcircles, of identical, or preferably different, radii, either joinedtogether directly or linked to each other by straight lines. Referringthis time to volumes, the combustion chamber may therefore comprise twospherical portions linked by an annular zone. Consideration may also begiven to an envelope substantially ovoid in volume. Of course, manyvariants may be envisaged, inspired by the latter one.

In the case of a burner suitable for an attenuating means of the spinnerdish type, again with the same conventions, the geometry of the cavityof the combustion chamber may be the following:

-   -   in horizontal section, its cross section may be approximately        annular;    -   in vertical section, its cross section may be of the type        described in respect of the burner associated with a spinneret.

The shape of the cavity defined by the combustion chamber mayfurthermore be such that it forces the stream of burnt gases to separateinto two streams near the expansion orifice: One stream is expelled viasaid orifice, while the other continues its path, especially in the formof a loop, in the combustion chamber.

Advantageously, the flame stabilizing element (or at least one of them,if there are more than one) is near both the internal wall of thecombustion chamber and the expansion orifice. Thus, the burnt gases maybe forced to circulate from one to the other, running along the wall ofthe chamber, choosing the longer path to achieve this.

Advantageously, to facilitate this circulation, most, or even all, ofthe shape of the internal wall of the chamber is curved (in a “vertical”plane within the meaning of the invention).

According to a variant of this embodiment, a deflector is interposedbetween the flame stabilizer and the expansion orifice, behind whichdeflector the oxidizer feed duct preferably runs. This deflector mayfulfill at least one of the following functions:

-   -   preventing the possibility of burnt gases emanating from the        confinement zone being expelled, having hardly emerged from this        zone, via the expansion orifice, thereby ensuring that they will        indeed follow a much longer path in the chamber before being        expelled;    -   guiding the oxidizer (air) toward the flame stabilizer, to avoid        any risk of this oxidizer possibly being engulfed in the        expansion orifice.

This detector may be an additional element, or may form an integral partof the internal wall of the combustion chamber by means of a suitableprofile. Preferably, the expansion orifice of the combustion chamberopens into an optional afterburner chamber. This chamber preferablyterminates in a lip lying at the end of a narrowing zone. The size andthe shape of the cross section of this lip, and its inclination, maythen be adjusted according to requirements.

Advantageously, the wall of the combustion chamber is in fact a doublewall. Within the latter may flow, at least in part of it, the oxidizer(generally air) that will feed the burner before being injected into thecombustion chamber: This promotes heat exchange between this gas and thechamber, allowing in particular said gas to be preheated. Provision mayalso be made for the combustion chamber to be equipped with externalcooling means. This may be, for example, a water box system.

The internal wall, and even preferably the entire double wall when thereis one, of the combustion chamber is advantageously made almost entirelyof metal: A burner whose combustion chamber is made of metal, forexample steel, has a longer lifetime, is easier to maintain and islighter than a conventional burner using many refractory materials ofthe silica-clay type.

The burners according to the invention may be used in various fiberizingprocesses. In the case of the process called internal fiberizing, use ismade of a spinner into which the material to be fiberized is poured, theperipheral band of said spinner being drilled with holes. Preferably,the material to be fiberized is firstly poured into a bowl drilled withholes and rotating at the same speed as the spinner, said holes allowingthe peripheral band of the spinner to be fed with the material. Toattenuate the cones of molten material emanating from said holes, thisspinner is provided with a system of annular burners that expel gas athigh velocity and at high temperature, as described in the patents citedin the preamble. In this particular case, a plurality of burnersaccording to the invention may therefore be provided, such that they canbe arranged concentrically around the spinner-type fiberizing machine.

In the case of a fiberizing process with attenuation using a spinneret,a single burner according to the invention, or several arranged in alinear fashion, may be used for providing the gas-induced attenuation ofthe fibers leaving the spinneret.

In the case of a fiberizing process using a spinner dish or a rotor fedwith molten glass, a burner according to the invention having an overallannular shape is used.

The combustion chamber may open into an afterburner chamber. Furthercombustion may take place in this afterburner chamber, due possibly tothe combustion of excess fuel coming from the combustion chamber.Further combustion may also be caused by introducing a certain amount offuel into the afterburner chamber via a suitable conduit.

A subject of the invention is also a conventional internal combustionburner, which would therefore have no flame stabilizer but whichprovides separate oxidizer and fuel feeds for the combustion chamberand/or the geometry of the combustion chamber of which would be thatdescribed above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in detail below with the aid of anon-limiting illustrative example, with the following figures:

FIG. 1: is a vertical sectional drawing of an annular burner accordingto the invention;

FIG. 2: is a horizontal sectional drawing of the burner according toFIG. 1;

FIG. 3: is a sectional drawing of the flame stabilizer used in thecombustion chamber of the burner according to FIGS. 1 and 2;

FIG. 4: is a representation of several stabilizers side by side in alinear-type burner; and

FIGS. 5 a, 5 b: are each a highly schematic representation of a spinnerthat can use the annular burner according to FIGS. 1 to 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

These figures are schematic, and not strictly to scale in order to makethem easier to examine. FIG. 1 therefore shows a burner according to theinvention in its entirety, in cross section in a vertical plane. Theburner is in the fiberizing position, around a spinner dish having avertical axis of rotation (not shown). This figure is only ahalf-section (the burner being axisymmetric about a vertical axis).

The combustion chamber 1 is defined by the wall 2, which defines a crosssection of ovoid shape. As will be more clearly understood from FIG. 3,which shows a partial cross section of the entire burner in a horizontalplane, the overall shape of the combustion chamber is annular. Thisburner is intended to be placed around a mineral wool spinner dish, soas to generate an annular curtain of hot gas participating in theattenuation of the filaments leaving the dish. This chamber is providedwith an expansion orifice 3 that opens into an afterburner chamber 4,also of annular shape. This chamber narrows at its end and terminates inan annular lip 5. An air feed is provided, this opening via a duct 6into the combustion chamber 1 after having flowed within the double wallof said chamber in order to preheat the air (the double wall is notshown). This stream of air is guided, by means of a deflector 7, to aflame stabilizer 8 shown in FIG 2. This stabilizer is a curved metalpiece placed very close to the internal wall of the combustion chamber1. FIG. 4 shows this in cross section: The air coming from the duct 6arrives behind this stabilizer and envelops it, going around it. Thisstabilizer 8 has two walls 8 a and 8 b substantially facing each otherand joined together at one of their ends by a curved end wall 8 c so asto form a semi-open opening zone 8 d opposite the end wall 8 c. Thisstabilizer 8 defines, between the walls and the inside of the semi-openzone, part of a confinement zone 10 in which the combustion takes place,this being shown in FIGS. 2 and 4 by a gray color. The combustible gasis injected via the outlet orifice or end 9 of a feed duct 13. This end9 is placed either inside the semi-open zone of the stabilizer, near theend wall 8 c, and/or in front of the stabilizer and off-center withrespect to the axis of symmetry of the stabilizer. The gas is thusinjected so that it is sprayed against the walls 8 a and 8 b and againstthe end wall 8 c of the stabilizer, and must then move back toward thefront of the stabilizer, running along the walls. This path thus allowsoptimum mixing of the gas with the air, to ensure complete combustion.In addition, this spraying against the walls of the stabilizer providesadditional cooling of said stabilizer.

A portion of the air will be trapped in the confinement zone 10 andmixed with the combustible gas, in order for the actual combustion totake place. FIG. 2 shows that two gas recirculation loops 11 and 12 arecreated in the confinement zone 10, these being shown symbolically bythe arrows. The combustion is almost entirely centered in the zone 13,i.e. the boundary between the two recirculation loops 11 and 12.

For a standard attenuating gas temperature, for example around 1400 to1600° C., the gas will be preferably injected via the end 9 located infront of the stabilizer, rather than close to the end wall of thestabilizer in the case of a cooler temperature of about 1200° C. Thus,the path traveled by the gas up to the walls 8 a, 8 b and the end wall 8c of the stabilizer and its return beyond the opening of the stabilizeris extended and the gas is perfectly mixed with the air in order toallow complete combustion.

The burnt gas resulting from the combustion is then expelled, along anaxis A, this being an axis of symmetry of the stabilizer 8 in the planeof the cross section shown in FIG. 2. Referring once more to FIG. 1,this burnt gas, because of the shape of the stabilizer 8, will thereforebe constrained to run along the wall of the combustion chamber 1 along alooped path shown symbolically by an arrow. The shape of the wall nearthe expansion orifice 3 is such that it forces this stream to separateinto two portions near this orifice: One portion of the stream continuesto “swirl” into the combustion chamber, while the remaining portion ofthe stream is expelled via this orifice 3. The shape of the combustionchamber therefore makes it possible to control this division of thestream, creating a head loss just upstream of the expansion orifice 3.

Before the air is introduced into the combustion chamber 1 via the duct6, it flows within the double wall of the combustion chamber (not shown)for heat exchange with the gas flowing in the chamber.

FIG. 3 shows the combustion chamber of the burner, in horizontal crosssection: It clearly has an annular shape, with a plurality ofstabilizers 8 spaced uniformly apart concentrically and arranged so thattheir confinement zones face toward the “outside” of the ring (that isto say the opposite side from its virtual center). The stabilizers inthis example are organized in two concentric rows. These stabilizers areuniformly spaced apart in each row. From one row to the other they areoffset in a staggered fashion: This offset spacing allows the inflows ofair to be able to feed air to cool the stabilizers of both rows at thesame time and to cool them appropriately. Each stabilizer is fixed inthe combustion chamber by mechanical means that allow its position to beadjusted and especially allow it to pivot so as to orient the flow ofburnt gases emanating from its confinement zone in various ways (bypivoting, especially with respect to a radial axis of the ring that thecombustion chamber forms, passing through the stabilizer in question).

In the configuration shown in FIG. 3, each stabilizer is placed suchthat the stream of gas escapes therefrom, in an approximately radialdirection toward the “outside” of the ring. The stabilizers may thus be“inclined”, especially all by the same angle relative to theabovementioned radial axis, thereby producing, as output from theburner, a tangential jet of gas.

Each of the stabilizers is provided, as described above, with an inflowof 9 to 100% fuel. However, as regards the inflow of oxidizer (air),provision may be made for a feed duct to spray air against severalstabilizers at the same time. There is thus a curtain of air generatedby a duct of suitable shape, which is capable of supplying fuel to atleast two stabilizers at the same time in the same row and/or placed onebehind the other in two different rows: The inflows of air are thusprovided for the first row of stabilizers (closest to the virtual centerof the ring), the excess air that they spray also reaching the secondrow. The spacing between two adjacent stabilizers in the same row isdesigned so that the streams of burnt gases that escape therefrom veryquickly join up, just “after” their respective confinement zones. Forgreater clarity, this is illustrated with the aid of FIG. 4 (in whichthe stabilizers are shown, for convenience, in a line, but the situationis similar when they are placed concentrically): This shows the air,indicated symbolically by the arrows, that strikes the adjacentstabilizers, and the streams of burnt gases emanating from each of them,merging as a single continuous sheet of gas output from the confinementzone.

The combustion chamber 1 is provided with a water box. The chamber ismade of metal, as is the stabilizer. A metal stabilizer may be “allowed”insofar as, when the burner is operating, its outer wall is permanentlyin contact with the relatively “cool” air coming from the duct 6.

A metal combustion chamber may also be “allowed”, provided that a systemof heat exchange with the feed air, possibly combined with a watercooling system (or another, equivalent system), has been organized. Ametal structure is a major advantage in terms of durability, compactnessand moderate manufacturing cost. Compared to the conventional internalcombustion burners used in the fiberizing field, this type of burner hasmuch greater operational flexibility.

Since there are separate inflows of air and combustible gas, the levelof safety is very high.

This burner also has a low inertia, and ensures a rapid response whenthe air and fuel flow rates are adjusted. These adjustments are easy tomake.

It allows a very wide temperature range of the gas output by the burner,from 200 to 1600° C., to be achieved. This is therefore a particularlyadvantageous burner for obtaining relatively “cool” gases, without anyrisk, unlike in conventional burners, of the flame detaching because ofexcessive dilution: The flame, within a wide air/fuel ratio range, canbe maintained in the confinement zone of the stabilizer.

With such a burner, the outgoing jet of gas is remarkably stable.

Its energy/heat efficiency is also good. It is further improved when thedouble-wall system is used, this operating as an effective heatexchanger.

The structure of the burner thus permits modifications that arerelatively easy to make. Thus, the profile of the lip 5 and of theafterburner chamber 4 may be modified, especially so as to obtain a jetof gas output at a variable angle of inclination.

This burner opens up new possibilities in fiberizing, most particularlyin “internal” fiberizing using a spinner described in the aforementionedpatents. As shown highly schematically in FIG. 5, a spinner 50 is fed atits center with molten glass 56 and provided with a peripheral band 51drilled with holes 52 distributed in rows. The material to be fiberizedis poured through a hollow shaft into a bowl 57 that is mechanicallyconnected to the spinner. The bowl 57 is itself provided with holes fromwhich the material to be fiberized is ejected toward the peripheral band51 when the spinner 50 and its bowl 57 are rotated. The zone 53 of theperipheral band has a shoulder and is sometimes called the “hot spot”,as it is at this point that the spinner is hottest.

The spinner 50 is equipped with the annular burner according to theinvention, which emits gases that will attenuate the conical streams ofmolten glass escaping from the holes 52 when the spinner 50 is rotatedabout its vertical axis. The other elements of the fiberizing plant,which, moreover, are known (especially the blowing ring 54 and themagnetic induction ring 55), will not be explained in detail.

Compared to a standard operation, the burner according to the inventionallows much greater flexibility in terms of the parameters for adjustingthe fiberizing by the spinner. These are especially the fiberizingtemperature range, the effectiveness of the gas-induced attenuation(flow rate, temperature of the gases emanating from the burner, etc.),the speed of rotation of the spinner, or the composition of thevitrifiable material to be fiberized.

Thus, compared to a standard operation, it is now possible to choose atemperature for the gas output by the burner that is markedly lower thanis customary, since this specific burner allows this, while maintaininga high ejection velocity (>100 m/s): Instead of having a gas temperatureof at least 1400° C., it is possible to have a gas temperature of atmost 1300° C., especially less than 1280° C., preferably between 1100and 1250° C. The attenuating gases may thus be “cooler”. At the sametime, it is possible to control the viscosity of the molten vitrifiablematerial output by the spinner, at the hot spot of the latter (zone 53)(at which point the viscosity is lowest), to values of around 1000poise, for example between 500 and 2000 poise, whereas in generalmarkedly higher values are obtained, of the order of 3000 poise, at thelow-viscosity point: Specifically, a less viscous molten glass istherefore obtained, this being more fluid and consequently easier toattenuate.

Among the preferred glasses that can be fiberized by internalcentrifuging with the burner according to the invention, mention may bemade of glasses of the borosilicate-soda-lime type, the typicalproperties of which are:

-   -   a temperature corresponding to a 1000-poise viscosity (T_(log3))        of between about 1020 and 1100° C., especially between 1050 and        1080° C.;    -   liquidus temperature (T_(liquidus)) between 900° C. and 950° C.

With this type of glass, for example, a hot spot temperature of at most1200° C., especially a temperature between 950 and 1150° C., especiallyaround 1050° C., is preferred. Compared to standard fiberizingconditions, there is a smaller temperature difference between thetemperature of the glass at the hot spot and the temperature of theattenuating gases output by the burner, especially a difference of onlyabout 100 to 200° C.

Advantageously, the temperature difference between the hot spot of thespinner and the bottom of the peripheral band (namely the lowermost rowof holes) is about 40 to 80° C.

It should be noted that, to maintain the steady-state operation of thespinner, at a lower viscosity, and at the same spinner feed rate(without any break in feed from the glass reserve upstream of thespinner), it is possible to adjust at least one of the following otherparameters: Reduction in the diameter of the holes in the peripheralband of the spinner (for example down to 0.1-0.3 mm) and/or to increasetheir number and/or adjust the speed of rotation of said spinner.

This novel method of operation has, in fact, two very beneficial effectson the quality of the fibers obtained. Firstly, the histogram of thesizes of the fibers obtained (especially the size assessed by theirmicronaire, in a known manner, and/or by their mean diameter) is tighterabout the average value: The histogram has schematically the shape of anarrower Gaussian, with a smaller standard deviation, especially onesubstantially equal to half the mean diameter. For example, it ispossible to have a standard deviation of about 2 microns for a meanfiber diameter of 4 microns (whereas the standard deviation is 3 or 4more for the same mean diameter with a standard burner, all other thingsbeing equal). Furthermore, it has been found that the fibers appear tobe softer to the touch, this being more pleasant for the operator who isinstalling the insulation wall and for the final user.

According to a second approach, a standard attenuation gas temperaturemay be maintained, for example around 1400 to 1600° C., but the flowrate of gas delivered by the burner may be modified/increased. Theburner according to the invention may, in fact, be markedly morepowerful than a conventional burner. This power may be quantified, inparticular, by the amount of fuel of the methane type that it consumesper unit time. A conventional annular burner of 200 mm diameter has apower, measured in this way, of about 15 to 20 m³/h, i.e. 0.75 to 1 m³of gas per hour and per mm of spinner diameter. The burner according tothe invention may achieve powers of at least 25, 30, 35 or even 40 m³/h,i.e. powers of at least 1.25, especially at least 1.5 or 1.75 or even 2Nm³ per hour and per mm of spinner diameter.

At the same time, the power of the burner may also be quantified by theoutput of gas delivered, which, in this technical field, is oftenexpressed by measuring a burner output pressure (which can be relativelyeasily measured by a Pitot tube), together with the width of the lip ofthe burner. In this case, pressures of at least 600 to 1000 mm of watercolumn may be achieved for a lip width of, for example, between 5 and 10mm, whereas the pressures obtained with conventional burners are more ofthe order of 400 to 500 mm of water column. With such gas flow rates, toprevent the fibers, once they have been ejected from the spinner, frombeing turned back onto the spinner and/or onto one another, from one rowof holes to the other, the speed of rotation of the spinner ismodified/increased at the same time.

The advantage of this method of operation with a high gas flow rate isthat the attenuation capacity of the spinner may be increased: Byincreasing the output per hole, that is, to say the number of kilogramsfiberized per spinner hole and per day, it is, overall, possible toincrease the output of the spinner. In particular, it is possible toachieve outputs of at least 1.2 to 1.5 kg per hole per day, whilemaintaining useful mean fiber dimensions, especially those correspondingto a fineness index expressed by a micronaire of 3 under 5 grams.

These two modes of operation are mentioned as an illustration, and theburner according to the invention allows different fiberizing parametersto be selected, and any compromise to be achieved between concerns forproductivity, ease of fiberizing and quality of the mineral woolobtained.

1. An internal combustion burner, comprising: a combustion chamber, intowhich at least one duct for feeding fuel and oxidizer opens, andprovided with an expansion orifice, wherein the combustion chamber isprovided with a plurality of flame stabilizing elements each having twosolid walls substantially facing each other and joined together at oneend by a solid end wall to constitute a semi-open opening zone oppositethe solid end wall, a confinement zone being created between the twosolid walls and near the opening zone, in which confinement zone atleast part of combustion between the oxidizer and fuel takes place;wherein the at least one duct is connected to feed ducts fed with a gascontaining one or more fuels and the feed ducts open via a plurality ofoutlet orifices for outputting said one or more fuels into saidconfinement zone, said plurality of outlet orifices being located suchthat each outlet orifice of said plurality is located between twoadjacent flame stabilizing elements and downstream from the adjacentflame stabilizing elements so as to be offset with respect to an axis ofsymmetry of each flame stabilizing element, wherein the at least oneduct includes a feed duct fed with gas containing the oxidizer and thatopens into the combustion chamber so as to spray the oxidizer on a sideof the walls of the flame stabilizing elements that is opposite a sidein direct contact with the confinement zone of the flame stabilizingelements, and wherein the plurality of flame stabilizing elements areeach placed near an internal wall of the combustion chamber.
 2. Theburner as claimed in claim 1, wherein at least a portion of thecombustion between the oxidizer and fuel takes place in the confinementzone created by the flame stabilizing elements.
 3. The burner as claimedin claim 1, wherein the combustion chamber comprises, in a horizontalplane, at least 5 flame stabilizing elements, placed beside one anotherwith a uniform spacing between two adjacent elements of the flamestabilizing elements.
 4. The burner as claimed in claim 3, wherein ahorizontal cross section of the combustion chamber is either ofparallelogram type, with a plurality of the flame stabilizing elementsbeing placed approximately in line, or of annular type, with a pluralityof the flame stabilizing elements being placed concentrically.
 5. Theburner as claimed in claim 1, wherein a vertical cross section of thecombustion chamber is at least partly curved and has at least onestabilizing element or plural stabilizing elements lying in distinctplanes.
 6. The burner as claimed in claim 1, wherein each of theplurality of flame stabilizing elements is predominantly made of metal.7. The burner as claimed in claim 1, wherein at least one of theplurality of flame stabilizing elements has a geometry with a symmetryin a plane and/or an axial symmetry, or with two symmetries in twoplanes perpendicular to each other.
 8. The burner as claimed in claim 7,wherein at least one of the plurality of flame stabilizing elements hasa projection perpendicular to one of its planes of symmetryapproximately in a form of a U or a V.
 9. The burner as claimed in claim7, wherein at least one of the plurality of flame stabilizing elementshas a projection perpendicular to one of the planes of symmetry thereofin an approximate shape of a triangle, or a triangle with roundedcorners, or an approximately isosceles triangle shape.
 10. The burner asclaimed in claim 1, wherein the feed duct opening into the confinementzone is at least partially fed with fuel.
 11. The burner as claimed inclaim 1, wherein the feed duct that opens into the combustion chamber tospray the oxidizer onto a side of the walls of the at least one flamestabilizing element that is opposite the side in direct contact with theconfinement zone, is at least partially fed with an air-type oxidizer.12. The burner as claimed in claim 1, wherein said at least one ductincludes an oxidizer feed duct and a fuel feed duct that are separatedfrom one another.
 13. The burner as claimed in claim 12, wherein theduct for feeding oxidizer and the duct for feeding fuel open into thecombustion chamber are positioned in proximity with at least one flamestabilizing element so that the confinement zone of the at least oneflame stabilizing element comprises both a mixing zone, for mixing anoxidizer with fuel, and a combustion zone.
 14. The burner as claimed inclaim 1, wherein the oxidizer and fuel are mixed in the combustionchamber.
 15. The burner as claimed in claim 1, wherein a position of atleast one of the plurality of flame stabilizing elements relative to aninternal wall of the combustion chamber forces burnt gases to run alongat least part of the internal wall.
 16. The burner as claimed in claim1, wherein an internal wall of the combustion chamber is profiled tomaximize a path of burnt gases emanating from the confinement zone of atleast one of the plurality of flame stabilizing elements.
 17. The burneras claimed in claim 1, wherein an internal wall of the combustionchamber is profiled to force a stream of burnt gases coming from theconfinement zone of at least one of the plurality of flame stabilizingelements to separate into first and second portions in proximity withthe expansion orifice, the first portion being expelled via said orificeand the second portion continuing its path, in a form of a loop, in thecombustion chamber.
 18. The burner as claimed in claim 1, wherein atleast one of the plurality of flame stabilizing elements is located inproximity with an internal wall of the combustion chamber in proximitywith the expansion orifice.
 19. The burner as claimed in claim 18,further comprising an oxidizer feed duct and a deflector elementinterposed between at least one of the plurality of flame stabilizingelements and the expansion orifice, behind which deflector said oxidizerfeed duct opens.
 20. The burner as claimed in claim 1, furthercomprising an afterburner chamber having a narrowing zone, wherein theexpansion orifice opens into said afterburner chamber, said afterburnerchamber terminating in a lip at an end of said narrowing zone of theafterburner chamber.
 21. The burner as claimed in claim 1, wherein awall of the combustion chamber comprises a double wall within which theoxidizer flows before opening out into the combustion chamber by the atleast one feed duct.
 22. The burner as claimed in claim 1, wherein aninternal wall of the combustion chamber is substantially made entirelyof metal.
 23. The burner as claimed in claim 1 wherein the combustionchamber is provided with external cooling means.
 24. The burner asclaimed in claim 1, wherein the burner is combined with a mineral woolfiberizing machine of a spinneret, spinner dish, or rotor type.
 25. Theburner as claimed in claim 1, wherein the burner is used in a mineralwool fiberizing machine of a spinneret type, having a spinner combinedwith a bowl or rotor.
 26. An internal combustion burner, comprising: acombustion chamber, into which at least one duet for feeding fuel andoxidizer opens, and provided with an expansion orifice, wherein thecombustion chamber is provided with a plurality of flame stabilizingelements each having two solid walls substantially facing each other andjoined together at one end by a solid end wall to constitute a semi-openopening zone opposite the solid end wall, a confinement zone beingcreated between the two solid walls and near the opening zone, in whichconfinement zone at least part of combustion between the oxidizer andfuel takes place; wherein the at least one duct is connected to feedducts fed with a gas containing one or more fuels and the feed ductsopen via a plurality of outlet orifices for outputting said one or morefuels into said confinement zone at a first velocity, said plurality ofoutlet orifices being located such that each outlet orifice of saidplurality is located between two adjacent flame stabilizing elements anddownstream from the adjacent flame stabilizing elements so as to beoffset with respect to an axis of symmetry of each flame stabilizingelement, wherein the at least one duct includes a feed duct fed with gascontaining the oxidizer and that opens into the combustion chamber so asto spray the oxidizer at a second velocity on a side of the walls of theflame stabilizing elements that is opposite a side in direct contactwith the confinement zone of the flame stabilizing elements, and whereinthe first velocity is higher than the second velocity, such that saidfuels flow from said plurality of outlet orifices to said confinementzone and the combustion occurs within the confinement zone.